The proposed research seeks to develop means to provide amputee patients with enhanced tactile sensation from their prostheses. This effort builds on previous work by using a chronic implanted multichannel microelectrode array to selectively activate individual sensory afferents in order to evoke more natural tactile percepts than has previously been demonstrated using more gross cuff or other electrode interfaces. The research comprises three main activities: 1) An existing multielectrode insertable device will be modified for stimulation of peripheral nerve axons and tested in animals to verify the design and implantation procedure. The animal studies will include analysis of somatosensory evoked potentials; responses to a conditioned behavioral paradigm; and histocompatibility. Stimulus selectivity, threshold stability, and neural damage over time will be evaluated from the animal. studies. 2) Following the initial animal work, we will implant electrode arrays in upper extremity amputee subjects for chronic evaluation. With these subjects we will optimize the stimulation patterns and parameters to maximize the naturalness of the evoked percepts. Differential qualities of contact, light touch, slippage, sustained force and graded skin force will be sought. other information that will be obtained from these studies will be the location, size and stability of the evoked "phantom" sensations and insight regarding the plasticity of the individual's sensory system before and following chronic electrical stimulation of the amputated nerves. 3) The outcome of this project will be a demonstration of the feasibility and desirability of performing microstimulation for sensory replacement in prostheses and design specifications for the implementation of permanent and effective microstimulation systems.